The present invention refers to the general field of sealing devices designed to reduce the flow sections between different cavities of a turbomachine, e.g. in the high-pressure turbine of a turbomachine.
In the hot portions of a turbomachine, sealing devices are subjected to considerable variations in clearance arising from general relative movements of casings, and from thermal distortions. In particular, when one of the portions of the turbomachine to be sealed is sectorised, as is the case in particular for the stator stages of the high-pressure turbine, the bearing zone of the sealing device is discontinuous, and sealing gaskets that are not sectorised become ineffective.
Different types of gaskets exist for sealing of the hot portions of a turbomachine. For example, so-called brush gaskets are known through U.S. Pat. Nos. 4,781,388, 5,480,162 and 6,170,831, said gaskets consisting of a plurality of bristles or wires, e.g. made of metal, which are crimped or welded and held, at one of their ends in a housing, while their free ends are in contact with the surface of the portion of the turbomachine that is to be sealed. Such brush joints are thus able to adapt to the variations in clearance to which the sealing devices are subjected. By construction, the bristles of a brush gasket adapt to the deformed or discontinuous surfaces of the portion that is to be sealed.
In static applications where the relative displacements of the zone that is to be sealed are small, it is known to make brush gaskets having bristles that present a disposition that is radial or axial. However, when relative movements are large, it is advantageous to be able to have recourse to an intermediate arrangement in which the bristles of the brush gasket are bent, as in U.S. Pat. No. 6,059,526, since that enables the bristles to be made to flex over a considerable length.
Nevertheless, the brush gasket presents certain drawbacks for static applications. Overall permeability of the bristles which constitute said gasket is too high to enable really effective sealing to be achieved. This observation is particularly true for those metal bristles which must have a diameter of more than 75 micrometers (μm) for the bristles to retain acceptable mechanical properties, as a function of the pressure differences to which said bristles are subjected.
Likewise, bent brush gaskets are not completely satisfactory. In particular, their overall permeability is always too high to guarantee perfect sealing of the zone that is to be sealed. Moreover, when the surface that is to be sealed presents discontinuities and/or deformations due, in particular, to relative radial and/or axial movements between the portions of the zone of the turbomachine that are to be sealed, bent brush gaskets do not fit closely over various geometrical roughnesses, which leads to large leakage areas under the brushes.